JBoss Security documentation (http://docs.jboss.com/jbossas/admindevel326/html/ch8.chapter.html) 
describes a RoleGroup concept for its DatabaseServerLoginModule.

Table Principals(PrincipalID text, Password text)
Table Roles(PrincipalID text, Role text, RoleGroup text)

What is the purpose of a RoleGroup and how is it used by JBoss?
How do you use it in ejb declarative security?